<!DOCTYPE html>



  


<html class="theme-next muse use-motion" lang="yulei">
<head>
  <meta charset="UTF-8"/>
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1"/>
<meta name="theme-color" content="#222">



  
  
    
    
  <script src="/lib/pace/pace.min.js?v=1.0.2"></script>
  <link href="/lib/pace/pace-theme-minimal.min.css?v=1.0.2" rel="stylesheet">







<meta http-equiv="Cache-Control" content="no-transform" />
<meta http-equiv="Cache-Control" content="no-siteapp" />















  
  
  <link href="/lib/fancybox/source/jquery.fancybox.css?v=2.1.5" rel="stylesheet" type="text/css" />




  
  
  
  

  
    
    
  

  

  

  

  

  
    
    
    <link href="//fonts.googleapis.com/css?family=Lato:300,300italic,400,400italic,700,700italic&subset=latin,latin-ext" rel="stylesheet" type="text/css">
  






<link href="/lib/font-awesome/css/font-awesome.min.css?v=4.6.2" rel="stylesheet" type="text/css" />

<link href="/css/main.css?v=5.1.2" rel="stylesheet" type="text/css" />


  <meta name="keywords" content="C,预处理," />








  <link rel="shortcut icon" type="image/x-icon" href="/favicon.ico?v=5.1.2" />






<meta name="description" content="一、一般用法我们使用#把宏参数变为一个字符串,用##把两个宏参数贴合在一起。 用法： 1234567891011#include &amp;lt;stdio.h&amp;gt;#define STR(s)      #s#define CONAS(a,b)  int(a##e##b)int main(void)&amp;#123;    printf( STR(hello) );          //输出字符串&quot;hel">
<meta name="keywords" content="C,预处理">
<meta property="og:type" content="article">
<meta property="og:title" content="C预处理中#号和##号的作用">
<meta property="og:url" content="http://yoursite.com/2017/05/10/C预处理中井号和井井号的作用/index.html">
<meta property="og:site_name" content="yuleisoochow">
<meta property="og:description" content="一、一般用法我们使用#把宏参数变为一个字符串,用##把两个宏参数贴合在一起。 用法： 1234567891011#include &amp;lt;stdio.h&amp;gt;#define STR(s)      #s#define CONAS(a,b)  int(a##e##b)int main(void)&amp;#123;    printf( STR(hello) );          //输出字符串&quot;hel">
<meta property="og:locale" content="yulei">
<meta property="og:updated_time" content="2017-09-19T11:47:34.728Z">
<meta name="twitter:card" content="summary">
<meta name="twitter:title" content="C预处理中#号和##号的作用">
<meta name="twitter:description" content="一、一般用法我们使用#把宏参数变为一个字符串,用##把两个宏参数贴合在一起。 用法： 1234567891011#include &amp;lt;stdio.h&amp;gt;#define STR(s)      #s#define CONAS(a,b)  int(a##e##b)int main(void)&amp;#123;    printf( STR(hello) );          //输出字符串&quot;hel">



<script type="text/javascript" id="hexo.configurations">
  var NexT = window.NexT || {};
  var CONFIG = {
    root: '/',
    scheme: 'Muse',
    sidebar: {"position":"left","display":"post","offset":12,"offset_float":12,"b2t":false,"scrollpercent":false,"onmobile":false},
    fancybox: true,
    tabs: true,
    motion: true,
    duoshuo: {
      userId: '0',
      author: '博主'
    },
    algolia: {
      applicationID: '',
      apiKey: '',
      indexName: '',
      hits: {"per_page":10},
      labels: {"input_placeholder":"Search for Posts","hits_empty":"We didn't find any results for the search: ${query}","hits_stats":"${hits} results found in ${time} ms"}
    }
  };
</script>



  <link rel="canonical" href="http://yoursite.com/2017/05/10/C预处理中井号和井井号的作用/"/>





  <title>C预处理中#号和##号的作用 | yuleisoochow</title>
  














</head>

<body itemscope itemtype="http://schema.org/WebPage" lang="yulei">

  
  
    
  

  <div class="container sidebar-position-left page-post-detail ">
    <div class="headband"></div>

    <header id="header" class="header" itemscope itemtype="http://schema.org/WPHeader">
      <div class="header-inner"><div class="site-brand-wrapper">
  <div class="site-meta ">
    

    <div class="custom-logo-site-title">
      <a href="/"  class="brand" rel="start">
        <span class="logo-line-before"><i></i></span>
        <span class="site-title">yuleisoochow</span>
        <span class="logo-line-after"><i></i></span>
      </a>
    </div>
      
        <p class="site-subtitle">一蓑烟雨，几度春秋</p>
      
  </div>

  <div class="site-nav-toggle">
    <button>
      <span class="btn-bar"></span>
      <span class="btn-bar"></span>
      <span class="btn-bar"></span>
    </button>
  </div>
</div>

<nav class="site-nav">
  

  
    <ul id="menu" class="menu">
      
        
        <li class="menu-item menu-item-home">
          <a href="/" rel="section">
            
              <i class="menu-item-icon fa fa-fw fa-home"></i> <br />
            
            首页
          </a>
        </li>
      
        
        <li class="menu-item menu-item-categories">
          <a href="/categories/" rel="section">
            
              <i class="menu-item-icon fa fa-fw fa-th"></i> <br />
            
            分类
          </a>
        </li>
      
        
        <li class="menu-item menu-item-about">
          <a href="/about/" rel="section">
            
              <i class="menu-item-icon fa fa-fw fa-user"></i> <br />
            
            关于
          </a>
        </li>
      
        
        <li class="menu-item menu-item-archives">
          <a href="/archives/" rel="section">
            
              <i class="menu-item-icon fa fa-fw fa-archive"></i> <br />
            
            归档
          </a>
        </li>
      
        
        <li class="menu-item menu-item-tags">
          <a href="/tags/" rel="section">
            
              <i class="menu-item-icon fa fa-fw fa-tags"></i> <br />
            
            标签
          </a>
        </li>
      

      
        <li class="menu-item menu-item-search">
          
            <a href="javascript:;" class="popup-trigger">
          
            
              <i class="menu-item-icon fa fa-search fa-fw"></i> <br />
            
            搜索
          </a>
        </li>
      
    </ul>
  

  
    <div class="site-search">
      
  <div class="popup search-popup local-search-popup">
  <div class="local-search-header clearfix">
    <span class="search-icon">
      <i class="fa fa-search"></i>
    </span>
    <span class="popup-btn-close">
      <i class="fa fa-times-circle"></i>
    </span>
    <div class="local-search-input-wrapper">
      <input autocomplete="off"
             placeholder="Searching..." spellcheck="false"
             type="text" id="local-search-input">
    </div>
  </div>
  <div id="local-search-result"></div>
</div>



    </div>
  
</nav>



 </div>
    </header>

    <main id="main" class="main">
      <div class="main-inner">
        <div class="content-wrap">
          <div id="content" class="content">
            

  <div id="posts" class="posts-expand">
    

  

  
  
  

  <article class="post post-type-normal" itemscope itemtype="http://schema.org/Article">
  
  
  
  <div class="post-block">
    <link itemprop="mainEntityOfPage" href="http://yoursite.com/2017/05/10/C预处理中井号和井井号的作用/">

    <span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
      <meta itemprop="name" content="yulei">
      <meta itemprop="description" content="">
      <meta itemprop="image" content="/uploads/head.png">
    </span>

    <span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
      <meta itemprop="name" content="yuleisoochow">
    </span>

    
      <header class="post-header">

        
        
          <h1 class="post-title" itemprop="name headline">C预处理中#号和##号的作用</h1>
        

        <div class="post-meta">
          <span class="post-time">
            
              <span class="post-meta-item-icon">
                <i class="fa fa-calendar-o"></i>
              </span>
              
                <span class="post-meta-item-text">Posted on</span>
              
              <time title="Post created" itemprop="dateCreated datePublished" datetime="2017-05-10T18:00:00+08:00">
                2017-05-10
              </time>
            

            

            
          </span>

          
            <span class="post-category" >
            
              <span class="post-meta-divider">|</span>
            
              <span class="post-meta-item-icon">
                <i class="fa fa-folder-o"></i>
              </span>
              
                <span class="post-meta-item-text">In</span>
              
              
                <span itemprop="about" itemscope itemtype="http://schema.org/Thing">
                  <a href="/categories/C/" itemprop="url" rel="index">
                    <span itemprop="name">C</span>
                  </a>
                </span>

                
                
              
            </span>
          

          
            
          

          
          

          

          
            <div class="post-wordcount">
              
                
                <span class="post-meta-item-icon">
                  <i class="fa fa-file-word-o"></i>
                </span>
                
                  <span class="post-meta-item-text">Words count in article</span>
                
                <span title="Words count in article">
                  763
                </span>
              

              
                <span class="post-meta-divider">|</span>
              

              
                <span class="post-meta-item-icon">
                  <i class="fa fa-clock-o"></i>
                </span>
                
                  <span class="post-meta-item-text">Reading time</span>
                
                <span title="Reading time">
                  4
                </span>
              
            </div>
          

          

        </div>
      </header>
    

    
    
    
    <div class="post-body" itemprop="articleBody">

      
      

      
        <h2 id="一、一般用法"><a href="#一、一般用法" class="headerlink" title="一、一般用法"></a>一、一般用法</h2><p>我们使用#把宏参数变为一个字符串,用##把两个宏参数贴合在一起。</p>
<p>用法：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div></pre></td><td class="code"><pre><div class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdio.h&gt;</span></span></div><div class="line"></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span> STR(s)      #s</span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span> CONAS(a,b)  int(a##e##b)</span></div><div class="line"></div><div class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">void</span>)</span></span></div><div class="line"><span class="function"></span>&#123;</div><div class="line">    <span class="built_in">printf</span>( STR(hello) );          <span class="comment">//输出字符串"hello"</span></div><div class="line">    <span class="built_in">printf</span>( <span class="string">"%d\n"</span>, CONS(<span class="number">2</span>,<span class="number">3</span>) );   <span class="comment">//2e3输出：2000</span></div><div class="line">    <span class="keyword">return</span> <span class="number">0</span>;</div><div class="line">&#125;</div></pre></td></tr></table></figure>
<a id="more"></a>
<h2 id="二、当宏参数是另一个宏的时候，需要注意的是凡宏里有用”-”或”-”的地方宏参数不会在展开"><a href="#二、当宏参数是另一个宏的时候，需要注意的是凡宏里有用”-”或”-”的地方宏参数不会在展开" class="headerlink" title="二、当宏参数是另一个宏的时候，需要注意的是凡宏里有用”#”或”##”的地方宏参数不会在展开"></a>二、当宏参数是另一个宏的时候，需要注意的是凡宏里有用”#”或”##”的地方宏参数不会在展开</h2><h3 id="1-非”-”和”-”的情况"><a href="#1-非”-”和”-”的情况" class="headerlink" title="1. 非”#”和”##”的情况"></a>1. 非”#”和”##”的情况</h3><figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div></pre></td><td class="code"><pre><div class="line"><span class="meta">#<span class="meta-keyword">define</span> TOW       (2)</span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span> MUL(a,b)  (a*b)</span></div><div class="line"></div><div class="line"><span class="built_in">printf</span>( <span class="string">"%d*%d=%d\n"</span>, TOW, TOW, MUL(TOW,TOW) );</div></pre></td></tr></table></figure>
<p>这行的宏会被展开为：<br><figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line"><span class="built_in">printf</span>( <span class="string">"%d*%d=%d\n"</span>, (<span class="number">2</span>), (<span class="number">2</span>), MUL((<span class="number">2</span>),(<span class="number">2</span>)) );</div></pre></td></tr></table></figure></p>
<p>MUL里的参数都会被展开为 <code>(2)</code> 。</p>
<h3 id="2-当有”-”和”-”的时候"><a href="#2-当有”-”和”-”的时候" class="headerlink" title="2. 当有”#”和”##”的时候"></a>2. 当有”#”和”##”的时候</h3><figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div></pre></td><td class="code"><pre><div class="line"><span class="meta">#<span class="meta-keyword">define</span> A         (2)</span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span> STR(s)    #s</span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span> CONS(a,b)  int(a##e##b)</span></div></pre></td></tr></table></figure>
<figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line"><span class="built_in">printf</span>( <span class="string">"int max: %s\n"</span> , STR(INT_MAX) ); <span class="comment">//INT_MAX是一个宏</span></div></pre></td></tr></table></figure>
<p>这行会被展开为：<br><figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line"><span class="built_in">printf</span>( <span class="string">"int max: %s\n"</span> , <span class="string">"INT_MAX"</span> );</div></pre></td></tr></table></figure></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line"><span class="built_in">printf</span>( <span class="string">"%s\n"</span> , CONS(A,A) );</div></pre></td></tr></table></figure>
<p>这一行则是：<br><figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line"><span class="built_in">printf</span>( <span class="string">"%s\n"</span> , <span class="keyword">int</span>(AeA) );     <span class="comment">//compile error</span></div></pre></td></tr></table></figure></p>
<p>INT_MAX和A都不会再被展开, 然而<strong>解决这个问题的方法很简单。加多一层中间转换宏。</strong></p>
<p><strong>加这层宏的用意是把所有宏的参数在这层里全部展开</strong>, 那么在转换宏里的那一个宏(_STR)就能得到正确的宏参数。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div></pre></td><td class="code"><pre><div class="line"><span class="meta">#<span class="meta-keyword">define</span> A            (2)</span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span> _STR(s)      #s</span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span> STR(s)       _STR(s)           <span class="comment">// 转换宏</span></span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span> _CONS(a,b)   int(a##e##b)</span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span> CONS(a,b)    _CONS(a,b)        <span class="comment">// 转换宏</span></span></div></pre></td></tr></table></figure>
<figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line"><span class="built_in">printf</span>( <span class="string">"int max: %s\n"</span> , STR(INT_MAX) );  <span class="comment">// INT_MAX,int型的最大值，为一个变量</span></div></pre></td></tr></table></figure>
<p>输出为：<code>int max: 0x7fffffff</code></p>
<p><code>STR(INT_MAX) --&gt;   _STR(0x7fffffff)</code> 然后再转换成字符串。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line"><span class="built_in">printf</span>(<span class="string">"%d\n"</span>, CONS(A, A));</div></pre></td></tr></table></figure>
<p>输出为：<code>200</code></p>
<p><code>CONS(A, A)   --&gt;   _CONS((2), (2))   --&gt; int((2)e(2))</code></p>
<h2 id="三、”-”和”-”的一些应用特例"><a href="#三、”-”和”-”的一些应用特例" class="headerlink" title="三、”#”和”##”的一些应用特例"></a>三、”#”和”##”的一些应用特例</h2><h3 id="1-合并匿名变量名称"><a href="#1-合并匿名变量名称" class="headerlink" title="1. 合并匿名变量名称"></a>1. 合并匿名变量名称</h3><figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div></pre></td><td class="code"><pre><div class="line"><span class="meta">#<span class="meta-keyword">define</span>   ___ANONYMOUS1(type, var, <span class="meta-keyword">line</span>)  type   var##<span class="meta-keyword">line</span></span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span>   __ANONYMOUS0(type, <span class="meta-keyword">line</span>)        ___ANONYMOUS1(type, _anonymous, <span class="meta-keyword">line</span>)</span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span>   ANONYMOUS(type)                 __ANONYMOUS0(type, __LINE__)</span></div></pre></td></tr></table></figure>
<p>例：<code>ANONYMOUS(static int);</code>   即: <code>static int _anonymous70;</code>   <code>70</code>表示该行行号；</p>
<p>第一层：<code>ANONYMOUS(static int);</code>   –&gt;   <code>__ANONYMOUS0(static int, __LINE__);</code></p>
<p>第二层：                           –&gt;   <code>___ANONYMOUS1(static int, _anonymous, 70);</code></p>
<p>第三层：                           –&gt;   <code>static int   _anonymous70;</code></p>
<p>即每次只能解开当前层的宏，所以<code>__LINE__</code>在第二层才能被解开；</p>
<h3 id="2-填充结构"><a href="#2-填充结构" class="headerlink" title="2. 填充结构"></a>2. 填充结构</h3><figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div></pre></td><td class="code"><pre><div class="line"><span class="meta">#<span class="meta-keyword">define</span>   FILL(a)    &#123;a, #a&#125;</span></div><div class="line"></div><div class="line"><span class="keyword">enum</span> IDD&#123;OPEN, CLOSE&#125;;</div><div class="line"><span class="keyword">typedef</span> <span class="class"><span class="keyword">struct</span> <span class="title">MSG</span>&#123;</span></div><div class="line">   IDD id;</div><div class="line">   <span class="keyword">const</span> <span class="keyword">char</span> * msg;</div><div class="line">&#125;MSG;</div></pre></td></tr></table></figure>
<figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">MSG _msg[] = &#123;FILL(OPEN), FILL(CLOSE)&#125;;</div></pre></td></tr></table></figure>
<p>相当于:<br><figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">MSG _msg[] = &#123;&#123;OPEN, <span class="string">"OPEN"</span>&#125;,&#123;CLOSE, <span class="string">"CLOSE"</span>&#125;&#125;;</div></pre></td></tr></table></figure></p>
<h3 id="3-记录文件名"><a href="#3-记录文件名" class="headerlink" title="3. 记录文件名"></a>3. 记录文件名</h3><figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div></pre></td><td class="code"><pre><div class="line"><span class="meta">#<span class="meta-keyword">define</span>   _GET_FILE_NAME(f)    #f</span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span>   GET_FILE_NAME(f)     _GET_FILE_NAME(f)</span></div><div class="line"><span class="keyword">static</span> <span class="keyword">char</span>   FILE_NAME[] = GET_FILE_NAME(__FILE__);</div></pre></td></tr></table></figure>
<h3 id="4-得到一个数值类型所对应的字符串缓冲大小"><a href="#4-得到一个数值类型所对应的字符串缓冲大小" class="headerlink" title="4. 得到一个数值类型所对应的字符串缓冲大小"></a>4. 得到一个数值类型所对应的字符串缓冲大小</h3><figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div></pre></td><td class="code"><pre><div class="line"><span class="meta">#<span class="meta-keyword">define</span>   _TYPE_BUF_SIZE(type)   sizeof #type</span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span>   TYPE_BUF_SIZE(type)    _TYPE_BUF_SIZE(type)</span></div><div class="line"><span class="keyword">char</span>   buf[TYPE_BUF_SIZE(INT_MAX)];</div></pre></td></tr></table></figure>
<pre><code>--&gt;   char   buf[_TYPE_BUF_SIZE(0x7fffffff)];
--&gt;   char   buf[sizeof &quot;0x7fffffff&quot;];
--&gt;   char   buf[11];
</code></pre><h3 id="5-用来定义一长串结构相似的函数"><a href="#5-用来定义一长串结构相似的函数" class="headerlink" title="5. 用来定义一长串结构相似的函数"></a>5. 用来定义一长串结构相似的函数</h3><figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div></pre></td><td class="code"><pre><div class="line"><span class="meta">#<span class="meta-keyword">define</span> CAL_WLAN_FUNC(funcname, uri) \</span></div><div class="line"><span class="keyword">char</span> *cal_wlan_get_#<span class="meta">#funcname(void) \</span></div><div class="line">&#123; \</div><div class="line">    <span class="keyword">static</span> wlan_buf[<span class="number">128</span>] = &#123;<span class="number">0</span>&#125;; \</div><div class="line">    <span class="built_in">memset</span>( wlan_buf, <span class="number">0</span>, <span class="keyword">sizeof</span>(wlan_buf) ); \</div><div class="line">    <span class="keyword">if</span>( get_value( uri, CAL_ID ) &lt; <span class="number">0</span> ) \</div><div class="line">        <span class="keyword">return</span> <span class="literal">NULL</span>; \</div><div class="line">    <span class="built_in">strcpy</span>( wlan_buf, wlan_buf_tmp ); \</div><div class="line">    <span class="keyword">return</span> wlan_buf; \</div><div class="line">&#125;</div><div class="line"></div><div class="line">CAL_WLAN_FUNC(enable, WLAN_ENABLE);</div><div class="line">CAL_WLAN_FUNC(bssid, WLAN_BSSID);</div><div class="line">CAL_WLAN_FUNC(channel, WLAN_CHANNEL);</div><div class="line">CAL_WLAN_FUNC(ssid, WLAN_SSID);</div><div class="line">CAL_WLAN_FUNC(key, WLAN_KEY);</div></pre></td></tr></table></figure>
<p>如上，通过宏来定义一串结构相似的函数，有效的减少代码量。</p>
<h2 id="四、一个简单的练习"><a href="#四、一个简单的练习" class="headerlink" title="四、一个简单的练习"></a>四、一个简单的练习</h2><figure class="highlight c"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div></pre></td><td class="code"><pre><div class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdio.h&gt;</span></span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span> f(a,b) a##b</span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span> g(a)  #a</span></div><div class="line"><span class="meta">#<span class="meta-keyword">define</span> h(a) g(a)</span></div><div class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">()</span></span></div><div class="line"><span class="function"></span>&#123;</div><div class="line">  <span class="built_in">printf</span>(<span class="string">"%s/n"</span>,h(f(<span class="number">1</span>,<span class="number">2</span>)));</div><div class="line">  <span class="built_in">printf</span>(<span class="string">"%s/n"</span>,g(f(<span class="number">1</span>,<span class="number">2</span>)));</div><div class="line">  <span class="keyword">return</span> <span class="number">0</span>;</div><div class="line">&#125;</div></pre></td></tr></table></figure>
<p>OUTPUT: 第一行:<code>12</code> 第二行:<code>f(1,2)</code></p>

      
    </div>
    
    
    

    

    
      <div>
        <div>
    
        <div style="text-align:center;color: #ccc;font-size:14px;">-------------本文结束<i class="fa fa-paw"></i>感谢您的阅读-------------</div>
    
</div>
      </div>
    

    

    

    <footer class="post-footer">
      
        <div class="post-tags">
          
            <a href="/tags/C/" rel="tag"><i class="fa fa-tag"></i> C</a>
          
            <a href="/tags/预处理/" rel="tag"><i class="fa fa-tag"></i> 预处理</a>
          
        </div>
      

      
      
      

      
        <div class="post-nav">
          <div class="post-nav-next post-nav-item">
            
              <a href="/2017/04/25/hexo设置多个deployment/" rel="next" title="hexo设置多个deployment">
                <i class="fa fa-chevron-left"></i> hexo设置多个deployment
              </a>
            
          </div>

          <span class="post-nav-divider"></span>

          <div class="post-nav-prev post-nav-item">
            
              <a href="/2017/08/22/多AP协调转向/" rel="prev" title="多AP协调转向">
                多AP协调转向 <i class="fa fa-chevron-right"></i>
              </a>
            
          </div>
        </div>
      

      
      
    </footer>
  </div>
  
  
  
  </article>



    <div class="post-spread">
      
    </div>
  </div>


          </div>
          


          
  <div class="comments" id="comments">
    
  </div>


        </div>
        
          
  
  <div class="sidebar-toggle">
    <div class="sidebar-toggle-line-wrap">
      <span class="sidebar-toggle-line sidebar-toggle-line-first"></span>
      <span class="sidebar-toggle-line sidebar-toggle-line-middle"></span>
      <span class="sidebar-toggle-line sidebar-toggle-line-last"></span>
    </div>
  </div>

  <aside id="sidebar" class="sidebar">
    
    <div class="sidebar-inner">

      

      
        <ul class="sidebar-nav motion-element">
          <li class="sidebar-nav-toc sidebar-nav-active" data-target="post-toc-wrap" >
            文章目录
          </li>
          <li class="sidebar-nav-overview" data-target="site-overview">
            站点概览
          </li>
        </ul>
      

      <section class="site-overview sidebar-panel">
        <div class="site-author motion-element" itemprop="author" itemscope itemtype="http://schema.org/Person">
          <img class="site-author-image" itemprop="image"
               src="/uploads/head.png"
               alt="yulei" />
          <p class="site-author-name" itemprop="name">yulei</p>
           
              <p class="site-description motion-element" itemprop="description">嵌入式领域的码农和coding爱好者</p>
          
        </div>
        <nav class="site-state motion-element">

          
            <div class="site-state-item site-state-posts">
              <a href="/archives/">
                <span class="site-state-item-count">12</span>
                <span class="site-state-item-name">日志</span>
              </a>
            </div>
          

          
            
            
            <div class="site-state-item site-state-categories">
              <a href="/categories/index.html">
                <span class="site-state-item-count">4</span>
                <span class="site-state-item-name">分类</span>
              </a>
            </div>
          

          
            
            
            <div class="site-state-item site-state-tags">
              <a href="/tags/index.html">
                <span class="site-state-item-count">10</span>
                <span class="site-state-item-name">标签</span>
              </a>
            </div>
          

        </nav>

        

        <div class="links-of-author motion-element">
          
            
              <span class="links-of-author-item">
                <a href="https://github.com/yuleisoochow" target="_blank" title="GitHub">
                  
                    <i class="fa fa-fw fa-github"></i>
                  
                    
                      GitHub
                    
                </a>
              </span>
            
          
        </div>

        
        

        
        

        


      </section>

      
      <!--noindex-->
        <section class="post-toc-wrap motion-element sidebar-panel sidebar-panel-active">
          <div class="post-toc">

            
              
            

            
              <div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-2"><a class="nav-link" href="#一、一般用法"><span class="nav-number">1.</span> <span class="nav-text">一、一般用法</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#二、当宏参数是另一个宏的时候，需要注意的是凡宏里有用”-”或”-”的地方宏参数不会在展开"><span class="nav-number">2.</span> <span class="nav-text">二、当宏参数是另一个宏的时候，需要注意的是凡宏里有用”#”或”##”的地方宏参数不会在展开</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#1-非”-”和”-”的情况"><span class="nav-number">2.1.</span> <span class="nav-text">1. 非”#”和”##”的情况</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#2-当有”-”和”-”的时候"><span class="nav-number">2.2.</span> <span class="nav-text">2. 当有”#”和”##”的时候</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#三、”-”和”-”的一些应用特例"><span class="nav-number">3.</span> <span class="nav-text">三、”#”和”##”的一些应用特例</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#1-合并匿名变量名称"><span class="nav-number">3.1.</span> <span class="nav-text">1. 合并匿名变量名称</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#2-填充结构"><span class="nav-number">3.2.</span> <span class="nav-text">2. 填充结构</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#3-记录文件名"><span class="nav-number">3.3.</span> <span class="nav-text">3. 记录文件名</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#4-得到一个数值类型所对应的字符串缓冲大小"><span class="nav-number">3.4.</span> <span class="nav-text">4. 得到一个数值类型所对应的字符串缓冲大小</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#5-用来定义一长串结构相似的函数"><span class="nav-number">3.5.</span> <span class="nav-text">5. 用来定义一长串结构相似的函数</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#四、一个简单的练习"><span class="nav-number">4.</span> <span class="nav-text">四、一个简单的练习</span></a></li></ol></div>
            

          </div>
        </section>
      <!--/noindex-->
      

      

    </div>
  </aside>


        
      </div>
    </main>

    <footer id="footer" class="footer">
      <div class="footer-inner">
        <div class="copyright" >
  
  &copy; 
  <span itemprop="copyrightYear">2017</span>
  <span class="with-love">
    <i class="fa fa-heart"></i>
  </span>
  <span class="author" itemprop="copyrightHolder">yulei</span>
</div>


<div class="powered-by">
  Powered by <a class="theme-link" href="https://hexo.io">Hexo</a>
</div>

<div class="theme-info">
  Theme -
  <a class="theme-link" href="https://github.com/iissnan/hexo-theme-next">
    NexT.Muse
  </a>
</div>


        

        
      </div>
    </footer>

    
      <div class="back-to-top">
        <i class="fa fa-arrow-up"></i>
        
      </div>
    

  </div>

  

<script type="text/javascript">
  if (Object.prototype.toString.call(window.Promise) !== '[object Function]') {
    window.Promise = null;
  }
</script>









  


  











  
  <script type="text/javascript" src="/lib/jquery/index.js?v=2.1.3"></script>

  
  <script type="text/javascript" src="/lib/fastclick/lib/fastclick.min.js?v=1.0.6"></script>

  
  <script type="text/javascript" src="/lib/jquery_lazyload/jquery.lazyload.js?v=1.9.7"></script>

  
  <script type="text/javascript" src="/lib/velocity/velocity.min.js?v=1.2.1"></script>

  
  <script type="text/javascript" src="/lib/velocity/velocity.ui.min.js?v=1.2.1"></script>

  
  <script type="text/javascript" src="/lib/fancybox/source/jquery.fancybox.pack.js?v=2.1.5"></script>

  
  <script type="text/javascript" src="/lib/canvas-nest/canvas-nest.min.js"></script>


  


  <script type="text/javascript" src="/js/src/utils.js?v=5.1.2"></script>

  <script type="text/javascript" src="/js/src/motion.js?v=5.1.2"></script>



  
  

  
  <script type="text/javascript" src="/js/src/scrollspy.js?v=5.1.2"></script>
<script type="text/javascript" src="/js/src/post-details.js?v=5.1.2"></script>



  


  <script type="text/javascript" src="/js/src/bootstrap.js?v=5.1.2"></script>



  


  




	





  





  






  

  <script type="text/javascript">
    // Popup Window;
    var isfetched = false;
    var isXml = true;
    // Search DB path;
    var search_path = "search.xml";
    if (search_path.length === 0) {
      search_path = "search.xml";
    } else if (/json$/i.test(search_path)) {
      isXml = false;
    }
    var path = "/" + search_path;
    // monitor main search box;

    var onPopupClose = function (e) {
      $('.popup').hide();
      $('#local-search-input').val('');
      $('.search-result-list').remove();
      $('#no-result').remove();
      $(".local-search-pop-overlay").remove();
      $('body').css('overflow', '');
    }

    function proceedsearch() {
      $("body")
        .append('<div class="search-popup-overlay local-search-pop-overlay"></div>')
        .css('overflow', 'hidden');
      $('.search-popup-overlay').click(onPopupClose);
      $('.popup').toggle();
      var $localSearchInput = $('#local-search-input');
      $localSearchInput.attr("autocapitalize", "none");
      $localSearchInput.attr("autocorrect", "off");
      $localSearchInput.focus();
    }

    // search function;
    var searchFunc = function(path, search_id, content_id) {
      'use strict';

      // start loading animation
      $("body")
        .append('<div class="search-popup-overlay local-search-pop-overlay">' +
          '<div id="search-loading-icon">' +
          '<i class="fa fa-spinner fa-pulse fa-5x fa-fw"></i>' +
          '</div>' +
          '</div>')
        .css('overflow', 'hidden');
      $("#search-loading-icon").css('margin', '20% auto 0 auto').css('text-align', 'center');

      $.ajax({
        url: path,
        dataType: isXml ? "xml" : "json",
        async: true,
        success: function(res) {
          // get the contents from search data
          isfetched = true;
          $('.popup').detach().appendTo('.header-inner');
          var datas = isXml ? $("entry", res).map(function() {
            return {
              title: $("title", this).text(),
              content: $("content",this).text(),
              url: $("url" , this).text()
            };
          }).get() : res;
          var input = document.getElementById(search_id);
          var resultContent = document.getElementById(content_id);
          var inputEventFunction = function() {
            var searchText = input.value.trim().toLowerCase();
            var keywords = searchText.split(/[\s\-]+/);
            if (keywords.length > 1) {
              keywords.push(searchText);
            }
            var resultItems = [];
            if (searchText.length > 0) {
              // perform local searching
              datas.forEach(function(data) {
                var isMatch = false;
                var hitCount = 0;
                var searchTextCount = 0;
                var title = data.title.trim();
                var titleInLowerCase = title.toLowerCase();
                var content = data.content.trim().replace(/<[^>]+>/g,"");
                var contentInLowerCase = content.toLowerCase();
                var articleUrl = decodeURIComponent(data.url);
                var indexOfTitle = [];
                var indexOfContent = [];
                // only match articles with not empty titles
                if(title != '') {
                  keywords.forEach(function(keyword) {
                    function getIndexByWord(word, text, caseSensitive) {
                      var wordLen = word.length;
                      if (wordLen === 0) {
                        return [];
                      }
                      var startPosition = 0, position = [], index = [];
                      if (!caseSensitive) {
                        text = text.toLowerCase();
                        word = word.toLowerCase();
                      }
                      while ((position = text.indexOf(word, startPosition)) > -1) {
                        index.push({position: position, word: word});
                        startPosition = position + wordLen;
                      }
                      return index;
                    }

                    indexOfTitle = indexOfTitle.concat(getIndexByWord(keyword, titleInLowerCase, false));
                    indexOfContent = indexOfContent.concat(getIndexByWord(keyword, contentInLowerCase, false));
                  });
                  if (indexOfTitle.length > 0 || indexOfContent.length > 0) {
                    isMatch = true;
                    hitCount = indexOfTitle.length + indexOfContent.length;
                  }
                }

                // show search results

                if (isMatch) {
                  // sort index by position of keyword

                  [indexOfTitle, indexOfContent].forEach(function (index) {
                    index.sort(function (itemLeft, itemRight) {
                      if (itemRight.position !== itemLeft.position) {
                        return itemRight.position - itemLeft.position;
                      } else {
                        return itemLeft.word.length - itemRight.word.length;
                      }
                    });
                  });

                  // merge hits into slices

                  function mergeIntoSlice(text, start, end, index) {
                    var item = index[index.length - 1];
                    var position = item.position;
                    var word = item.word;
                    var hits = [];
                    var searchTextCountInSlice = 0;
                    while (position + word.length <= end && index.length != 0) {
                      if (word === searchText) {
                        searchTextCountInSlice++;
                      }
                      hits.push({position: position, length: word.length});
                      var wordEnd = position + word.length;

                      // move to next position of hit

                      index.pop();
                      while (index.length != 0) {
                        item = index[index.length - 1];
                        position = item.position;
                        word = item.word;
                        if (wordEnd > position) {
                          index.pop();
                        } else {
                          break;
                        }
                      }
                    }
                    searchTextCount += searchTextCountInSlice;
                    return {
                      hits: hits,
                      start: start,
                      end: end,
                      searchTextCount: searchTextCountInSlice
                    };
                  }

                  var slicesOfTitle = [];
                  if (indexOfTitle.length != 0) {
                    slicesOfTitle.push(mergeIntoSlice(title, 0, title.length, indexOfTitle));
                  }

                  var slicesOfContent = [];
                  while (indexOfContent.length != 0) {
                    var item = indexOfContent[indexOfContent.length - 1];
                    var position = item.position;
                    var word = item.word;
                    // cut out 100 characters
                    var start = position - 20;
                    var end = position + 80;
                    if(start < 0){
                      start = 0;
                    }
                    if (end < position + word.length) {
                      end = position + word.length;
                    }
                    if(end > content.length){
                      end = content.length;
                    }
                    slicesOfContent.push(mergeIntoSlice(content, start, end, indexOfContent));
                  }

                  // sort slices in content by search text's count and hits' count

                  slicesOfContent.sort(function (sliceLeft, sliceRight) {
                    if (sliceLeft.searchTextCount !== sliceRight.searchTextCount) {
                      return sliceRight.searchTextCount - sliceLeft.searchTextCount;
                    } else if (sliceLeft.hits.length !== sliceRight.hits.length) {
                      return sliceRight.hits.length - sliceLeft.hits.length;
                    } else {
                      return sliceLeft.start - sliceRight.start;
                    }
                  });

                  // select top N slices in content

                  var upperBound = parseInt('1');
                  if (upperBound >= 0) {
                    slicesOfContent = slicesOfContent.slice(0, upperBound);
                  }

                  // highlight title and content

                  function highlightKeyword(text, slice) {
                    var result = '';
                    var prevEnd = slice.start;
                    slice.hits.forEach(function (hit) {
                      result += text.substring(prevEnd, hit.position);
                      var end = hit.position + hit.length;
                      result += '<b class="search-keyword">' + text.substring(hit.position, end) + '</b>';
                      prevEnd = end;
                    });
                    result += text.substring(prevEnd, slice.end);
                    return result;
                  }

                  var resultItem = '';

                  if (slicesOfTitle.length != 0) {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + highlightKeyword(title, slicesOfTitle[0]) + "</a>";
                  } else {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + title + "</a>";
                  }

                  slicesOfContent.forEach(function (slice) {
                    resultItem += "<a href='" + articleUrl + "'>" +
                      "<p class=\"search-result\">" + highlightKeyword(content, slice) +
                      "...</p>" + "</a>";
                  });

                  resultItem += "</li>";
                  resultItems.push({
                    item: resultItem,
                    searchTextCount: searchTextCount,
                    hitCount: hitCount,
                    id: resultItems.length
                  });
                }
              })
            };
            if (keywords.length === 1 && keywords[0] === "") {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-search fa-5x" /></div>'
            } else if (resultItems.length === 0) {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-frown-o fa-5x" /></div>'
            } else {
              resultItems.sort(function (resultLeft, resultRight) {
                if (resultLeft.searchTextCount !== resultRight.searchTextCount) {
                  return resultRight.searchTextCount - resultLeft.searchTextCount;
                } else if (resultLeft.hitCount !== resultRight.hitCount) {
                  return resultRight.hitCount - resultLeft.hitCount;
                } else {
                  return resultRight.id - resultLeft.id;
                }
              });
              var searchResultList = '<ul class=\"search-result-list\">';
              resultItems.forEach(function (result) {
                searchResultList += result.item;
              })
              searchResultList += "</ul>";
              resultContent.innerHTML = searchResultList;
            }
          }

          if ('auto' === 'auto') {
            input.addEventListener('input', inputEventFunction);
          } else {
            $('.search-icon').click(inputEventFunction);
            input.addEventListener('keypress', function (event) {
              if (event.keyCode === 13) {
                inputEventFunction();
              }
            });
          }

          // remove loading animation
          $(".local-search-pop-overlay").remove();
          $('body').css('overflow', '');

          proceedsearch();
        }
      });
    }

    // handle and trigger popup window;
    $('.popup-trigger').click(function(e) {
      e.stopPropagation();
      if (isfetched === false) {
        searchFunc(path, 'local-search-input', 'local-search-result');
      } else {
        proceedsearch();
      };
    });

    $('.popup-btn-close').click(onPopupClose);
    $('.popup').click(function(e){
      e.stopPropagation();
    });
    $(document).on('keyup', function (event) {
      var shouldDismissSearchPopup = event.which === 27 &&
        $('.search-popup').is(':visible');
      if (shouldDismissSearchPopup) {
        onPopupClose();
      }
    });
  </script>





  

  

  

  

  

  

</body>
</html>
